Miles's Taste Tests for 12AX7
OverviewI got four new 12AX7 tubes from Lord Valve for comparison purposes. I also had some barely used Chinese tubes, and some older tubes as well. I compared them in two small amps from the 60s.
- Chinese 12AX7/ECC83 (slightly used, only markings are tube numbers in red)
- GE 7025 (USA) (old and used hard)
- Realistic 12AX7/ECC83 (labeled "Long-life" and "USA")
- US made 12AX7A (labeled R.T.N.)
EquipmentI used two amps, a Kalamazoo Model One and a Silvertone 1263. The Kalamazoo uses a single 12AX7 preamp tube and a 6BQ5 (EL84) output tube, has one channel with volume and tone controls, and a single, 10" speaker. I also tried it through the 4 ohm 2-12 Scorpion pair of a Peavey Heritage VTX combo.
The Silvertone came with three 7025's, two for preamps and one for tremolo, and has two 6V6's (slightly used RCA black glass) for output. It has two channels, with volume and tone on each channel, and a wimpy tremolo. I ran it through the 4 ohm 2-12 Scorpion pair of a Peavey Heritage VTX combo.
Both amps use tube rectifiers, multistage capacitor/resistor power supply filters, and point to point wiring.
The primary guitar was a Hagstrom 1 with two DiMarzio SDS-1s and completely flexible pickup selection. I also tried a BC Rich ST Platinum with a humbucker in the bridge slot.
CaveatsNo, these aren't the most popular amps. But there are plenty of tests that tell you what works in Fenders and Marshalls, already. These are representative of lower end amps you might find at garage sales, pawn shops, eBay, or in your parents' attic.
Tubes can make quite a difference, but so can everything else. In particular, the output transformer and speaker are at least as important as which tube you use. The differences between tubes in the Kalamazoo were not as apparent as in the Silvertone until I hooked the Kalamazoo to the Scorpion speakers.
Finally, these were more snacks than meals, first impressions only. I played with each tube for maybe five minutes.
ResultsThere wasn't a real clear winner, although there was a clear loser.
- US made 12AX7A - Good bottom end, could use a bit more top end. (This is the original tube; it had more top end once upon a time.) Plenty of volume. Good crunchy sound when overdriven. Worked really well in the Kalamazoo.
- EI ECC83 - Not quite the output of the other tubes, and slightly less bottom end. Very bright when overdriven. Seemed to favor single coils pickups.
- GE JAN 12AX7WA - Not quite the output of the other tubes, and slightly less high end. Good bottom end, excellent midrange. Very warm sounding, excellent dynamics, but not quite the clarity on chords of the best tubes. Overdrive a bit weak sounding.
- Ruby 12AX7A-C (Selected) - Sounded excellent with single coil pickups. Good bottom and midrange on the clean sound, and the high end really kicked in on overdrive.
- Sovtek 12AX7LPS - Similar to the original US made 12AX7A. Good definition, especially at cleaner volumes, but not a lot of high end at that volume. Really likes humbuckers. Good crunch sound. When overdriven, it has tons of bottom end, and the highs punch through.
- Chinese 12AX7/ECC83 - Lowest output. At low, clean volumes, excellent clarity but no bottom end. When overdriven, too shrill, almost no definition, and still missing a bit of bottom end.
- GE 7025 (USA) - These were the original tubes for the Silvertone, AFAIK. They were all extremely microphonic by the time I got them, and generated random hisses, crackles and pops. But they still sounded really good, otherwise - good definition, good overdrive. All the top end you could use, lacked a bit of bottom end, but that may have been age. If it weren't for the noise, I'd probably have just kept using these in the Silvertone.
- Realistic 12AX7/ECC83 - Old tube, usage unknown. Little bottom end, little top end, no clarity, far less output than the others. Since this was not an original tube in the parts amp I recovered it from, there's no way of knowing how much usage it had seen, but it looks newer than most of the other used tubes.
RankingsIf you can find the GE 7025 or R.T.N. 12AX7A (whatever that is) in NOS, you are probably set. Of current production tubes, I give the Sovtek 12AX7LPS a slight advantage with humbuckers, with the Ruby 12AX7A-C Selected second, but about even for single coil pickups. The EI ECC83 and GE JAN 12AX7WA were slightly behind both, but are still nice tubes. The unbranded generic Chinese tubes are fairly useless for a classic rock sound, but would work well for low volume clean sound (jazz, maybe) if you don't need any low end. I would only use the Realistic 12AX7/ECC83 in something like a tremolo oscillator - and then only if I were desperate.
I'd use any of the four newer tubes in the Kalamazoo, but in reality the original R.T.N. 12AX7A is still doing a fine job. I'm happy with the three newer tubes in the Silvertone, set up like this: Ruby 12AX7A-C Selected in the trem channel, Sovtek 12AX7LPS on the second channel (1 triode for each input), and the EI ECC83 in the mixer/inverter socket. I've more or less settled on the Sovtek 12AX7LPS for my Kalamazoo Model Two.
Other NotesThe Ruby appeared to be identical in construction to the cheap Chinese tubes. My guess is that Ruby simply takes the best of the lot and rebrands them (this has been confirmed by multiple sources -Miles). This would imply horrible quality control - but given the Chinese approach to mass manufacturing (volume over everything), this would not be a surprise.
The generic Chinese tubes were all pulled from new amplifiers that didn't sound right to their owners. Apparently some of the manufacturers aren't worrying about putting good tubes in their amps these days.
These results were first posted in the alt.guitar.amps newsgroup.
Last updated: 24 July 2000
Taste Test copyrighted 1999 by Miles O'Neal, Austin, TX. Incidentals copyright 1999 Miles O'Neal, Austin, TX. All rights reserved. Miles O'Neal <meo@XYZZY.rru.com> [remove the "XYZZY." to make things work!] c/o RNN / 1705 Oak Forest Dr / Round Rock, TX / 78681-1514